Magnetrons



C. H. DIX ET AL MAGNETRONS Aug. 11, 1959 2 Sheets-Sheet 1 Filed March20, 1957 Fl T' ORNEYS Aug. 11, 1959 c. H. DIX ET AL 2,399,604

MAGNETRONS Filed March 20, 1957 2 Sheets-Sheet 2 Fig.2.

BYLQLLQIZZLLAQQQ FITTQRN 6 5 United States Patent M MAGNETRONS CyrilHenry Dix, Kenton, and Vincent Albert Heathcote, Fnlham, London,England, assignors to The M-O Valve Company Limited, London, EnglandApplication March 20, 1957, Serial No. 647,289

Claims priority, application Great Britain March 28, 1956 5 Claims. (Cl.31539.75)

This invention relates to magnetrons of the type having a cylindricalmetal anode chamber within which is supported an anode system comprisinga plurality of cavity resonators spaced round the anode axis, the latterbeing substantially parallel to, and usually coincident with, the axisof the anode chamber, in which a cylindrical cathode is supported so asto lie coaxially within the anode system, and in which each end of theanode chamber is closed by the sealing thereto of a pole-piece ofmagnetic material designed to co-operate with an external magnet forproducing within the anode system the axial magnetic field required forthe operation of the magnetron.

A magnetron of the type specified is often required to co-operate with apermanent magnet in the form of an incomplete ring, the pole-pieces ofthe magnetron forming a continuation of the two ends of the magnet sothat the anode system of the magnetron lies in the path of the magneticflux between these two ends.

In View of the intense magnetic field required for the operation of themagnetron, the ring magnet required is usually very bulky and heavy, butfor many purposes, such as for airborne use of the magnetron, it is verydesirable that the bulk and weight of the apparatus should be as small.as possible. The pole-pieces used hitherto in magnetrons of the typespecified have usually been of generally cylindrical shape, in somecases with the inner ends, that is to say the ends nearer the anodesystem, tapered for concentrating the magnetic field within the anodesystem.

We have now discovered that by using pole-pieces of a novel shape, it ispossible to use a smaller external permanent magnet whilst stillobtaining an operating axial magnetic field of the required strength,thereby reducing the bulk and weight of the apparatus. The invention canalso be applied with advantage where the external magnet is anelectro-rnagnet, as will be explained.

According to the invention, in a magnetron of the type specified theouter end of each pole-piece is bevelled so that the outer end face ofeach pole-piece is inclined to a plane perpendicular to the axis of theanode with the longer sides of the two pole-pieces lying on the sameside of the anode.

With a magnetron constructed in accordance with the invention, bycausing the longer sides of the pole-pieces to co-operate withcorresponding shaped ends of the external gapped-ring magnet, the effectof the bevelling is that the pole-pieces form more nearly a continuationwithin the magnetron of the surface curvature of the ring magnet, andthis results in much less stray magnetic flux being present at theseends than is obtained when the ends of the pole-pieces are perpendicularto the anode axis, as has been the case in magnetrons of the typespecified used hitherto. The reduction of stray flux means that more ofthe magnetic flux'is usefully employed for forming the operating axialmagnetic field within the anode system, and this in turn means that asmaller magnet can be used for obtaining a given axial 2,899,604Patented Aug. 11, 1959 field, with consequent reduction in the size andweight of the apparatus as a whole.

The bevelling of the ends of the pole-pieces can conveniently beeffected by forming the end faces of the pole-pieces as plane bevels,preferably equally inclined to a central plane passing through thecenter of the anode system perpendicularly to the axis of the anode. Forobtaining the optimum results, however, curved bevels could be used thatcause the pole-pieces to form more nearly continuations of the surfacecurvature of an approximately toroidal ring magnet with which themagnetron is intended to be used. The pole-pieces are preferably mirrorimages of each other, at least as regards their magnetic properties, inthe said central plane.

The invention includes within its scope combinations of magnetrons inaccordance with the invention as aforesaid with gapped-ring magnets,which may be either permanent magnets or electro-magnets. The advantageobtained with the invention in the latter case is either that the sizeof the magnet core can be reduced, 01' that the magnetising currentrequired in the windings of the magnet, for obtaining a given axialmagnetic field for the operation of the magnetron, can be reduced.

Preferably the thickness of the magnet in the direction perpendicular tothe axis of the anode is greater than the diameter of the pole-pieces inthis direction, and the two ends of the magnet are formed with recesses,extending parallel to the said axis, which fit closely round the partsof the pole-pieces of the magnetron about their longer sidesrwhen thepole-pieces are inserted into the recesses.

The pole-pieces of a magnetron in accordnace with the invention need notnecessarily consist of a single piece of magnetic material. Thus in somecases one or both of the pole-pieces might be pierced by a hole, coaxialwith the anode axis, along which passes a tube providing a support andlead for the cathode, and within it a further tube or a rod providing asupport and lead for the cathode heater. The pole-piece might then beformed with one or more annular inserts of magnetic material between thevarious parts, which inserts are spaced apart for electricallyinsulating parts of the magnetron from each other. The bevelled end ofthe pole-piece is then to be regarded as applied to the surfaceenveloping all the parts of the pole-piece.

One embodiment of the invention will now be described by way of examplewith reference to the accompanying schematic drawing, in which Figure 1shows a section along the axis of a magnetron in accordance with theinvention, in operative combination with an approximately toroidalgapped-ring permanent magnet, and

Figure 2. shows a section along the line X'-X in Figure 1, looking fromthe right.

In this magnetron, the anode chamber is formed as a circular cylindricalhole within a square metal block 1, the ends of which hole are closed bymetal plates 2, 3 carrying pole-pieces 4, 5, which are of generallycircular cylindrical cross section at their inner ends and will befurther described later.

The central part of the block 1 is shaped to provide an even pluralityof inwardly projecting anode segments 6, which define between them thecavity resonators of the anode system and bound at their inner ends acircular cylindrical electron orbit space within which lies the cathode7 of the magnetron.

The cathode consists of a hollow metal tube of circular cross-sectioncoated externally with electron emissive material (not shown) and isspigoted into one end of a hole pierced through a generally cylindricalinner part 8 of the pole-piece 4, which part is carried by one end of acathode support tube 9 which extends away from the anode chambercoaxially with the anode axis. The

tube 9is insulatingly supported from the outer end of a metal tube 10,which coaxially surrounds it, by means of a glass thimble seal 11, andthe tube 10 is in turn supported .by the spigoting of its inner end intothe general: 1y cylindrical outer part 12 of the pole-piece'4.

The cathode 7 contains a heater 13 which is attached at one end to ametal disc 14 closing the free end of the cathode and at the other to astout support wire 15. The outer end of the wire 15 is coiled round, andwelded to, the reduced diameter end of a heater support rod 16, thecoiling providing resilience for the mounting and thermal expansion ofthe heater. The heater rod 16 is insulatingly supported from, andcoaxially within, the cathode support tube 9 by means of a glass buttonseal 17 at its outer end, and an insulating spacer 18 at an intermediatepoint along its length.

The outer end of the rod 16 projects beyond the glass button 17 toprovide a heater lead terminal, and the outer end of the tube 9 projectsbeyond the thimble 11 and is outwardly flanged, with the attachment of ametal reinforcing annulus 19, to provide the cathode lead terminal.

The pole-piece 4 made up of the two parts 8 and 12 has the general formof a circular cylinder, the outer part of which has been cut away by aplane inclined to a plane perpendicular to the anode axis to provide aplane bevelled outer end 20.

The pole-piece 5 is formed in one piece with its end face 21 similarlyplane-bevelled, so that the longer sides 22. and 23 of the twopole-pieces lie on the same side of the anode, and is provided on itsinner face with an annular recess 24 which magnetically simulates theeffect of the spacing between the parts 8 and 12 of the polepiece 4 forincreasing the uniformity of the axial magnetic field. The pole-piece 5is also pierced axially by a central hole into the outer end of which isspigotted a metal tube 25 which serves as a pumping stem and is closedby a cold-weld cut-01f in the manufacture of the magnetron. The tube 25is covered by a protective metal cap 26 attached to the bevelled outerend of the polepiece 5.

The anode system of the magnetron formed by the segments 6 is providedon each side with concentric pairs of metal mode-spacing rings 27, andan output coupling loop 28 is connected on each side of the anode to oneof these rings. The two arms of the loop 28 pass through holes formed inthe side of the anode block 1 and the centre of the loop is supported bya rod 29, set into the outer wall of the block, so as to lie within thespace bounded by a tube 30 spigoted into an apertured metal plate 31attached to the side of the block, the tube 30 being closed by a glassdome seal 32.

The block 1 is provided with channels 33 for the passage of water forcooling the anode in operation of the magnetron.

The metal parts of the magnetron referred to are all non-magnetic exceptfor the pole-pieces 4 and S.

The magnetron described is designed for co-operation with anapproximately toroidal ring permanent magnet 34 and is shown in thedrawing in operative combination with the magnet.

The magnet is of approximately rectangular crosssection reducing in areatowards the ends, the faces of which ends lie parallel to each other andare separated by a space just sutficient to permit the anode block 1 tobe inserted between them, as shown in the drawing.

The ends of the magnet are formed with cylindrical transverse recesses35 designed to receive the longer sides 22 and 23 of the pole-pieces 4.and 5 and to be a snug fit round approximatly half the circumference ofthe polepieces. The axial length of each of the recesses 35 is such thatthe longer sides 22, 23 of the magnet polepieces just extend to theouter surface of the magnet, and the bevelled end faces 20, 21 of thepole-pieces form approximate continuations of the curvature of the outerpart of the surface of the ring magnet that reduce the stray flux fromthe magnet toa low value.

We claim:

1. A magnetron having a cylindrical metal anode chamber, a plurality ofanode segments extending inmounted coaxially within the electron orbitspace, and

two pole-pieces of magnetic material each sealed into a different end ofthe anode chamber for closing the chamber and projecting outwards forengagement with an external magnet for producing within the anode systemthe axial magnetic field required for the operation of the magnetron,each pole-piece having its outer end face bevelled and the bevels beingoppositely directed so that the longer sides of the two pole-pieces lieon the same side of the anode.

2. A magnetron according to claim 1 wherein the two pole-pieces haveplane-bevelledouter end faces.

3. A magnetron according to claim 1 wherein in planes perpendicular tothe anode axis the pole-pieces are of semi-circular cross-section attheir longer sides so as to be insertable into a groove of semi-circularbottom shape formed across the gapped end of a toroidal ring magnet.

4. A magnetron according to claim 1 wherein at least one pole-piece isbuilt up by a plurality of coaxial pieces of magnetic material sealedbetween, and spaced apart by, the anode chamber and the cathode assemblysupport and supply leads, and wherein the surface enveloping all thesaid pole-piece parts has a bevelled outer end face as aforesaid.

5. The combination of a magnetron according to claim 1 with a gappedring magnet to the ends of which the longer sides of the magnetronpole-pieces are fitted so that the bevelled ends of the pole-piecesprovide approximate continuations of the general curvature of theexternal surface of the ring magnet.

References Cited in the file of this patent UNITED STATES PATENTS2,232,559 Rice Feb. 18, 1941 2,524,252 Brown Oct. 3, 1950 2,716,711Thompson Aug. 30, 1955 2,777,085 Gleason Jan. 8, 1957 2,787,728Crapuchettes Apr. 2, 1957

